Positive electrode materials for high discharge capacity lithium ion batteries

ABSTRACT

Positive electrode active materials are described that have a high tap density and high specific discharge capacity upon cycling at room temperature and at a moderate discharge rate. Some materials of interest have the formula Li 1+x Ni α Mn β Co γ O 2 , where x ranges from about 0.05 to about 0.25, α ranges from about 0.1 to about 0.4, β ranges from about 0.4 to about 0.65, and γ ranges from about 0.05 to about 0.3. The materials can be coated with a metal fluoride to improve the performance of the materials especially upon cycling. Also, the coated materials can exhibit a very significant decrease in the irreversible capacity lose upon the first charge and discharge of the battery.

FIELD OF THE INVENTION

The invention relates to positive electrode active materials for lithiumsecondary batteries that provide high tap density and high specificdischarge capacities. Furthermore, the invention relates to highspecific discharge capacity compositions with a metal fluoride coatingthat significantly stabilizes and increases the discharge capacityduring cycling. In general, the positive electrode materials andcompositions have high specific capacity with a layered structure andhigh tap density.

BACKGROUND OF THE INVENTION

Lithium batteries are widely used in consumer electronics due to theirrelatively high energy density. Rechargeable batteries are also referredto as secondary batteries, and lithium ion secondary batteries generallyhave a negative electrode material that intercalates lithium. For somecurrent commercial batteries, the negative electrode material can begraphite, and the positive electrode material can comprise lithiumcobalt oxide (LiCoO₂). In practice, only roughly 50% of the theoreticalcapacity of the cathode can be used, e.g., roughly 140 mAh/g. At leasttwo other lithium-based cathode materials are also currently incommercial use. These two materials are LiMn₂O₄, having a spinelstructure, and LiFePO₄, having an olivine structure. These othermaterials have not provided any significant improvements in energydensity.

Lithium ion batteries are generally classified into two categories basedon their application. The first category involves high power battery,whereby lithium ion battery cells are designed to deliver high current(Amperes) for such applications as power tools and Hybrid ElectricVehicles (HEVs). However, by design, these battery cells are lower inenergy since a design providing for high current generally reduces totalenergy that can be delivered from the battery. The second designcategory involves high energy batteries, whereby lithium ion batterycells are designed to deliver low to moderate current (Amperes) for suchapplications as cellular phones, lap-top computers, Electric Vehicles(EVs) and Plug in Hybrid Electric Vehicles (PHEVs) with the delivery ofhigher total capacity.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to positive electrode activematerial for lithium ion battery. The material generally has a 10^(th)cycle specific discharge capacity of at least 235 mAh/g at roomtemperature and a tap density of at least 1.8 g/mL. The specificdischarge capacity is determined at a discharge rate of C/3 whendischarged from 4.6 volts to 2.0 volts. In some embodiments, thepositive electrode active material comprises a composition with aformula of xLiMO₂·(1−x) Li₂M′O₃, where M represents one or more metalions having an average valance of +3 and M′ represents one or more metalions having an average valance of +4 and 0<x<1. For example, M′ cancomprise Mn and M can comprise Mn, Co and Ni. In some other embodiments,the positive electrode active material comprises a first material havingthe formula xLiMO₂ (1−x) Li₂M′O₃ and a metal fluoride coating of thesaid material.

In further embodiments, the positive electrode material comprises acomposition with a formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)M″_(δ)O_(2−z)F_(z),where x ranges from about 0.05 to about 0.25, a ranges from about 0.1 toabout 0.4, β ranges from about 0.4 to about 0.65, γ ranges from about0.05 to about 0.3, δ ranges from about 0 to about 0.1 and z ranges fromabout 0 to about 0.1, and where M″ is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce,Y, Nb or combinations thereof. The positive electrode material cancomprise a composition with a formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)O₂,where x ranges from about 0.05 to about 0.25, α ranges from about 0.1 toabout 0.4, β ranges from about 0.4 to about 0.65, and γ ranges fromabout 0.05 to about 0.3. In one embodiment, the material comprises acomposition with a formula Li_(1.2)Ni_(0.175)Co_(0.10)Mn_(0.525)O₂.

In some embodiments, the positive electrode active material comprisesfrom about 0.1 mole percent to about 4 mole percent metal fluoride,which can be a coating material. In particular, the metal fluoride cancomprise AlF₃ In some embodiments, the positive electrode activematerial has a 10^(th) cycle specific discharge capacity from about 240mAh/g to about 310 mAh/g at room temperature. In additional embodiments,the positive electrode active material has a 10^(th) cycle specificdischarge capacity from about 250 mAh/g to about 290 mAh/g at roomtemperature. The specific discharge capacity is determined at adischarge rate of C/3 when discharged from 4.6 volts to 2.0 volts. Insome embodiments, the material has a tap density of at least 2.0 g/mL.

In another aspect, the invention is related to a positive electrodeactive material for a lithium ion battery comprises a layered lithiummetal oxide composite comprising +4 metal cations, +3 metal cations and+2 metal cations within a crystalline lattice and a metal/metalloidfluoride coating on said composite. The first cycle irreversiblecapacity loss of the material is no more than about ⅔ of the first cycleirreversible capacity loss of the uncoated layered lithium metal oxidecomposite, when both are cycled at discharge rate of C/10. The 20^(th)cycle discharge capacity of the material is at least about 98% of the5th cycle discharge capacity when discharged at room temperature at adischarge rate of C/3. Additionally, the material can have a tap densityof at least 1.8 g/mL.

In some embodiments, the uncoated layered lithium metal oxide compositehas a formula of xLiMO₂ (1−x) Li₂M′O₃, where M represents one or moremetal ions having an average valance of +3 and M′ represents one or moremetal ions having an average valance of +4, 0<x<l. For example, the M′can comprise Mn and M can comprise Mn, Co and Ni. In furtherembodiments, the positive electrode material has a formulaLi_(1+x)Ni_(α)Mn_(β)Co_(γ)M_(δ)O_(2−z)F_(z), where x ranges from about0.05 to about 0.25, α ranges from about 0.1 to about 0.4, β ranges fromabout 0.4 to about 0.65, γ ranges from about 0.05 to about 0.3, δ rangesfrom about 0 to about 0.1 and z ranges from about 0 to about 0.1, andwhere M is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb or combinationsthereof. In some embodiments, the positive electrode active material cancomprise from about 0.1 mole percent to about 4 mole percent metalfluoride, which can be in the form of a coating. In particular, themetal fluoride can comprise AlF₃.

In some embodiments, the positive electrode active material has a 20thcycle discharge capacity that is at least about 98.5% of the 5th cycledischarge capacity when discharged at room temperature at a dischargerate of C/3. The 10th cycle discharge capacity of the material can befrom about 250 mAh/g to about 310 mAh/g at room temperature at adischarge rate of C/3 when discharged from 4.6 volts to 2.0 volts. Inadditional embodiments, the material has a 10^(th) cycle specificdischarge capacity of at least 260 mAh/g at room temperature. In oneembodiment, the material has a tap density of at least 2.0 g/mL.

A secondary lithium ion battery can be constructed using a positiveelectrode comprising the positive electrode active material disclosedherein, a negative electrode comprising a lithium intercalationcomposition and a separator between the positive electrode and thenegative electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a battery structure separated from acontainer.

FIG. 2 is a set of optical microscope images of metal carbonateprecursor particles from example 1 using a) a 20× and b) a 40×microscope objective, showing morphology of the particles.

FIG. 3 is a set of SEM micrographs of the lithium metal oxide samplefrom example 1 at two different magnifications, showing morphology ofthe particles.

FIG. 4 is an X-ray diffraction pattern of the uncoated lithium metaloxide sample from example 1, showing characteristic of a rock-salt typestructure.

FIG. 5 is a plot of the first cycle charge/discharge voltage versusspecific capacities of a battery formed from the sample materialdescribed in example 1 cycled at a discharge rate of (a) 0.1 C and (b)0.33 C respectively in the voltage range of 2.0V-4.6 V.

FIG. 6 is a plot of specific capacity versus cycle life for the batteryof FIG. 5, showing variation of the discharge capacities as a functionof cycle number.

FIG. 7 is an X-ray diffraction pattern of a 1.0 mole % aluminum fluoridecoated lithium metal oxide formed from the process of example 2, showingcharacteristic of a rock-salt type structure.

FIG. 8 is a plot of the first cycle charge/discharge voltage versusspecific capacities of a battery formed from the sample materialdescribed in example 2 cycled at a discharge rate of (a) 0.1 C and (b)0.33 C, respectively in the voltage range of 2.0V-4.6 V.

FIG. 9 is a set of plots of specific capacity versus cycle life of thesame battery of FIG. 8 showing variation of the discharge capacities asa function of cycle number.

FIG. 10 is a set of plots of specific capacity versus cycle life ofbatteries formed from the sample material described in example 2 alongwith the sample material described in example 1, i.e. a 1.0 mole %aluminum fluoride coated metal oxide as well as uncoated metal oxide,respectively.

DETAILED DESCRIPTION OF THE INVENTIONS

Lithium ion batteries described herein achieved improved cyclingperformance while exhibiting high specific capacity and high overallcapacity. High specific capacity and high overall capacity positiveelectrode materials are produced using techniques that yield improvedmaterial performance based on techniques that are scalable forcommercial production. Suitable synthesis techniques include, forexample, co-precipitation approaches. The stoichiometries of thematerials of particular interest have desirable properties forcommercial applications. The materials have excellent cycling propertiesand overall capacity as a result of a relatively high tap densitycombined with a high specific capacity. Use of a metal fluoride coatingor other suitable coatings provides further cycling enhancement. Thepositive electrode materials also exhibit a high average voltage over adischarge cycle so that the batteries have high power output along witha high specific capacity. As a result of the high tap density andexcellent cycling performance, the battery exhibit continuing high totalcapacity when cycled. Furthermore, the positive electrode materialsdemonstrate a reduced proportion of irreversible capacity loss after thefirst charge and discharge of the battery so that negative electrodematerial can be correspondingly reduced if desired. The combination ofexcellent cycling performance, high specific capacity, and high overallcapacity make these resulting lithium ion batteries an improved powersource, particularly for high energy applications, such as electricvehicles, plug in hybrid vehicles and the like.

The batteries described herein are lithium ion batteries in which anon-aqueous electrolyte solution comprises lithium ions. For secondarylithium ion batteries, lithium ions are released from the negativeelectrode during discharge such that the negative electrode functions asan anode during discharge with the generation of electrons from theoxidation of lithium upon its release from the electrode.Correspondingly, the positive electrode takes up lithium ions throughintercalation or a similar process during discharge such that thepositive electrode functions as a cathode which consumes electronsduring discharge. Upon recharging of the secondary battery, the flow oflithium ions is reversed through the battery with the negative electrodetaking up lithium and with the positive electrode releasing lithium aslithium ions.

The lithium ion batteries can use a positive electrode active materialthat is lithium rich relative to a reference homogenous electroactivelithium metal oxide composition. While not wanted to be limited bytheory, it is believed that appropriately formed lithium-rich lithiummetal oxides have a composite crystal structure. For example, in someembodiments of lithium rich materials, a Li₂MnO₃ material may bestructurally integrated with either a layered LiMnO₂ component orsimilar composite compositions with the manganese cations substitutedwith other transition metal cations with appropriate oxidation states.In some embodiments, the positive electrode material can be representedin two component notation as x Li₂MO₃·(1−x)LiM′O₂ where M′ is one ormore metal cations with an average valance of +3 with at least onecation being Mn⁺³ or Ni⁺³ and where M is one or more metal cations withan average valance of +4. These compositions are described further, forexample, in U.S. Pat. No. 6,680,143 to Thackeray et al., entitled“Lithium Metal Oxide Electrodes for Lithium Cells and Batteries,”incorporated herein by reference. Positive electrode active materials ofparticular interest have a formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)M_(δ)O_(2−z)F_(z), where x ranges from about 0.05 toabout 0.25, α ranges from about 0.1 to about 0.4, β range from about 0.4to about 0.65, γ ranges from about 0.05 to about 0.3, 6 ranges fromabout 0 to about 0.1 and z ranges from about 0 to about 0.1, and where Mis Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb or combinations thereof. Inparticular, surprisingly good results have been obtained forLi[Li_(0.2)Ni_(0.175)Co_(0.10)Mn_(0.525)]O₂, as presented in theexamples below for materials synthesized using a carbonateco-precipitation process. High specific capacities with low tapdensities were obtained for this composition using other synthesisapproaches as described in U.S. application Ser. No. 12/246,814 toVenkatachalam et al. entitled “Positive Electrode Material for LithiumIon Batteries Having a High Specific Discharge Capacity and Processesfor the Synthesis of these Materials”, incorporated herein by reference.These compositions have a low risk of fire for improved safetyproperties due to their specific compositions with a layered structureand reduced amounts of nickel relative to some other high capacitycathode materials. These compositions use low amounts of elements thatare less desirable from an environmental perspective, and can beproduced from starting materials that have reasonable cost forcommercial scale production.

The word “element” is used herein in its conventional way as referringto a member of the periodic table in which the element has theappropriate oxidation state if the element is in a composition and inwhich the element is in its elemental form, M⁰, only when stated to bein an elemental form. Therefore, a metal element generally is only in ametallic state in its elemental form or a corresponding alloy of themetal's elemental form. In other words, a metal oxide or other metalcomposition, other than metal alloys, generally is not metallic.

Thackeray et al. in the '143 patent describe the synthesis of layeredlithium-rich lithium metal oxides using solid state reactions. Somelithium-rich materials with exclusively lithium, nickel and manganesemetals have been formed using a carbonate co-precipitation approach, asdescribed in Lee et al., “High capacity Li[Li_(0.2)Ni_(0.2)Mn_(0.6)]O₂cathode materials via a carbonate co-precipitation method,” J. of PowerSources, 162(2006), 1346-1350, incorporated herein by reference. Kang etal. also describes a carbonate co-precipitation process in U.S. Pat. No.7,435,402 (the '402 patent) entitled “Method and Apparatus forPreparation of Spherical Metal Carbonates and Lithium Metal Oxides forLithium Rechargeable Batteries”, incorporated herein by reference. Inthe '402 patent to Kang et al., the lithium metal oxide materialssynthesized from the carbonate co-precipitation process has moderatespecific capacity performance. A carbonate co-precipitation process hasbeen performed for the desired lithium rich metal oxide materialsdescribed herein having cobalt in the composition and exhibiting thehigh specific capacity performance. In addition to the high specificactivity, the materials exhibit superior tap density which leads to highoverall capacity of the material in fixed volume applications.

As described herein, improved performance has been obtained usingco-precipitation approaches with a carbonate intermediate composition,and generally a solution is formed from which a metal carbonate isprecipitated with the desired metal stoichiometry. The metal carbonatecompositions from co-precipitation can be subsequently heat-treated toform the corresponding metal oxide composition with appropriatecrystallinity. The lithium cations can either be incorporated into theinitial co-precipitation process, or the lithium can be introduced in asolid state reaction during or following the heat treatment to form theoxide compositions from the carbonate compositions. As demonstrated inthe examples below, the resulting lithium rich metal oxide materialsformed with the co-precipitation process have improved performanceproperties. When the corresponding batteries with theintercalation-based positive electrode active materials are in use, theintercalation and release of lithium ions from the lattice induceschanges in the crystalline lattice of the electroactive material. Aslong as these changes are essentially reversible, the capacity of thematerial does not change. However, the capacity of the active materialsis observed to decrease with cycling to varying degrees. Thus, after anumber of cycles, the performance of the battery falls below acceptablevalues, and the battery is replaced. Also, on the first cycle of thebattery, generally there is an irreversible capacity loss that issignificantly greater than per cycle capacity loss at subsequent cycles.The irreversible capacity loss is the difference between the chargecapacity of the new battery and the first discharge capacity. Tocompensate for this first cycle irreversible capacity loss, extraelectroactive material is included in the negative electrode such thatthe battery can be fully charged even though this lost capacity is notaccessible during most of the life of the battery so that negativeelectrode material is essentially wasted. The bulk of the first cycleirreversible capacity loss is generally attributed to the positiveelectrode material.

Appropriate coating materials can both improve the long term cyclingperformance of the material as well as decrease the first cycleirreversible capacity loss. While not wanting to be limited by theory,the coatings may stabilize the crystal lattice during the uptake andrelease of lithium ions so that irreversible changes in the crystallattice are reduced significantly. In particular, metal fluoridecompositions can be used as effective coatings. The general use of metalfluoride compositions as coatings for cathode active materials,specifically LiCoO₂ and LiMn₂O₄, is described in published PCTapplication WO 2006/109930A to Sun et al., entitled “Cathode ActiveMaterial Coated with Fluorine Compound for Lithium Secondary Batteriesand Method for Preparing the Same,” incorporated herein by reference.

It has been discovered that metal fluoride coatings can providesignificant improvements for lithium rich layered positive electrodeactive materials described herein. These improvements relate to longterm cycling with significantly reduced degradation of capacity, asignificant decrease in first cycle irreversible capacity loss and animprovement in the capacity generally. The amount of coating materialcan be selected to accentuate the observed performance improvements.

As described herein, the lithium rich positive electrode activematerials with the composite crystal structure can exhibit high specificcapacity above 235 mAh/g at room temperature with good cyclingproperties for discharge from 4.6 volts and high tap density above 1.8g/mL. In general, when specific capacities are comparable, a higher tapdensity of a positive electrode material results in a higher overallcapacity of a battery. A positive electrode material described hereinwith high tap density in addition to high specific capacity thereforecan be used to construct batteries with significantly improvedperformance. It is important to note that during charge/dischargemeasurements, the specific capacity of a material depends on the rate ofdischarge. The maximum specific capacity of a particular material ismeasured at very slow discharge rates. In actual use, the actualspecific capacity is less than the maximum due to discharge at a finiterate. More realistic specific capacities can be measured usingreasonable rates of discharge that are more similar to the rates duringuse. For low to moderate rate applications, a reasonable testing rateinvolves a discharge of the battery over three hours. In conventionalnotation this is written as C/3 or 0.33 C. The positive electrode activematerials described herein can have a specific discharge capacity of atleast about 250 mAh/g at a discharge rate of C/10 at room temperaturewhen discharged from 4.6 volts and tap density above 1.8 g/mL.

Rechargeable batteries have a range of uses, such as mobilecommunication devices, such as phones, mobile entertainment devices,such as MP3 players and televisions, portable computers, combinations ofthese devices that are finding wide use, as well as transportationdevices, such as automobiles and fork lifts. Most of the batteries usedin these electronic devices have a fixed volume. It is therefore highlydesirable that the positive electrode material used in these batterieshas a high tap density so there is essentially more chargeable materialin the positive electrode yielding a higher total capacity of thebattery. The batteries described herein that incorporate improvedpositive electrode active materials with respect to specific capacity,tap density, and cycling can provide improved performance for consumers,especially for medium current applications.

Battery Structure

Referring to FIG. 1, a battery 100 is shown schematically having anegative electrode 102, a positive electrode 104 and a separator 106between negative electrode 102 and positive electrode 104. A battery cancomprise multiple positive electrodes and multiple negative electrodes,such as in a stack, with appropriately placed separators. Electrolyte incontact with the electrodes provides ionic conductivity through theseparator between electrodes of opposite polarity. A battery generallycomprises current collectors 108, 110 associated respectively withnegative electrode 102 and positive electrode 104.

Lithium has been used in both primary and secondary batteries. Anattractive feature of lithium metal is its light weight and the factthat it is the most electropositive metal, and aspects of these featurescan be advantageously captured in lithium ion batteries also. Certainforms of metals, metal oxides, and carbon materials are known toincorporate lithium ions into its structure through intercalation orsimilar mechanisms. Desirable mixed metal oxides are described furtherherein to function as electroactive materials for positive electrodes insecondary lithium ion batteries. Lithium ion batteries refer tobatteries in which the negative electrode active material is also alithium intercalation material. If lithium metal itself is used as theanode, the resulting battery generally is simply referred to as alithium battery.

The nature of the negative electrode intercalation material influencesthe resulting voltage of the battery since the voltage is the differencebetween the half cell potentials at the cathode and anode. Suitablenegative electrode lithium intercalation compositions can include, forexample, graphite, synthetic graphite, coke, fullerenes, niobiumpentoxide, tin alloys, silicon, titanium oxide, tin oxide, and lithiumtitanium oxide, such as Li_(x)TiO₂, 0.5<x≦1 or Li_(1+x)Ti_(2−x)O₄,0≦x≦⅓. Additional negative electrode materials are described incopending provisional patent applications Ser. No. 61/113,445 to Kumar,entitled “Inter-metallic Compositions, Negative Electrodes withInter-Metallic Compositions and Batteries,” and Ser. No. 61/125,476 toKumar et al., entitled “Lithium Ion Batteries with Particular NegativeElectrode Compositions,” both of which are incorporated herein byreference.

The positive electrode active compositions and negative electrode activecompositions generally are powder compositions that are held together inthe corresponding electrode with a polymer binder. The binder providesionic conductivity to the active particles when in contact with theelectrolyte. Suitable polymer binders include, for example,polyvinylidine fluoride, polyethylene oxide, polyethylene,polypropylene, polytetrafluoroethylene, polyacrylates,ethylene-(propylene-diene monomer) copolymer (EPDM) and mixtures andcopolymers thereof.

The particle loading in the binder can be large, such as greater thanabout 80 weight percent. To form the electrode, the powders can beblended with the polymer in a suitable liquid, such as a solvent for thepolymer. The resulting paste can be pressed into the electrodestructure.

The positive electrode composition, and possibly the negative electrodecomposition, generally also comprises an electrically conductive powderdistinct from the electroactive composition. Suitable supplementalelectrically conductive powders include, for example, graphite, carbonblack, metal powders, such as silver powders, metal fibers, such asstainless steel fibers, and the like, and combinations thereof.Generally, a positive electrode can comprise from about 1 weight percentto about 25 weight percent, and in further embodiments from about 2weight percent to about 15 weight percent distinct electricallyconductive powder. A person of ordinary skill in the art will recognizethat additional ranges of amounts of electrically conductive powderswithin the explicit ranges above are contemplated and are within thepresent disclosure.

The electrode generally is associated with an electrically conductivecurrent collector to facilitate the flow of electrons between theelectrode and an exterior circuit. The current collector can comprisemetal, such as a metal foil or a metal grid. In some embodiments, thecurrent collector can be formed from nickel, aluminum, stainless steel,copper or the like. The electrode material can be cast as a thin filmonto the current collector. The electrode material with the currentcollector can then be dried, for example in an oven, to remove solventfrom the electrode. In some embodiments, the dried electrode material incontact with the current collector foil or other structure can besubjected to a pressure from about 2 to about 10 kg/cm² (kilograms persquare centimeter).

The separator is located between the positive electrode and the negativeelectrode. The separator is electrically insulating while providing forat least selected ion conduction between the two electrodes. A varietyof materials can be used as separators. For example, glass fibers formedinto a porous mat can be used as a separator. Commercial separatormaterials are generally formed from polymers, such as polyethyleneand/or polypropylene that are porous sheets that provide for ionicconduction. Commercial polymer separators include, for example, theCelgard® line of separator material from Hoechst Celanese, Charlotte,N.C.

Electrolytes for lithium ion batteries can comprise one or more selectedlithium salts. Appropriate lithium salts generally have inert anions.Suitable lithium salts include, for example, lithiumhexafluorophosphate, lithium hexafluoroarsenate, lithiumbis(trifluoromethyl sulfonyl imide), lithium trifluoromethane sulfonate,lithium tris(trifluoromethyl sulfonyl) methide, lithiumtetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate,lithium chloride and combinations thereof. Traditionally, theelectrolyte comprises a 1 M concentration of the lithium salts.

For lithium ion batteries of interest, a non-aqueous liquid is generallyused to dissolve the lithium salt(s). The solvent is generally inert anddoes not dissolve the electroactive materials. Appropriate solventsinclude, for example, propylene carbonate, dimethyl carbonate, diethylcarbonate, 2-methyl tetrahydrofuran, dioxolane, tetrahydrofuran, methylethyl carbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile,formamide, dimethyl formamide, triglyme (tri(ethylene glycol) dimethylether), diglyme (diethylene glycol dimethyl ether), DME (glyme or1,2-dimethyloxyethane or ethylene glycol dimethyl ether), nitromethaneand mixtures thereof.

The electrodes described herein can be incorporated into variouscommercial battery designs. For example, the cathode compositions can beused for prismatic shaped batteries, wound cylindrical batteries, coinbatteries or other reasonable battery shapes. The testing in theExamples is performed using coin cell batteries. The batteries cancomprise a single cathode structure or a plurality of cathode structuresassembled in parallel and/or series electrical connection(s). While thepositive electrode active materials can be used in batteries forprimary, or single charge use, the resulting batteries generally havedesirable cycling properties for secondary battery use over multiplecycling of the batteries.

In some embodiments, the positive electrode and negative electrode canbe stacked with the separator between them, and the resulting stackedstructure can be rolled into a cylindrical or prismatic configuration toform the battery structure. Appropriate electrically conductive tabs canbe welded or the like to the current collectors, and the resultingjellyroll structure can be placed into a metal canister or polymerpackage, with the negative tab and positive tab welded to appropriateexternal contacts. Electrolyte is added to the canister, and thecanister is sealed to complete the battery. Some presently usedrechargeable commercial batteries include, for example, the cylindrical18650 batteries (18 mm in diameter and 65 mm long) and 26700 batteries(26 mm in diameter and 70 mm long), although other battery sizes can beused.

Positive Electrode Active Materials

The positive electrode active materials comprise lithium intercalatingmetal oxide compositions. In some embodiments, the lithium metal oxidecompositions can comprise lithium rich compositions that generally arebelieved to form a layered composite structure. The positive electrodeactive compositions can exhibit surprisingly high specific capacitiesand high tap densities in lithium ion battery cells under realisticdischarge conditions. The desired electrode active materials can besynthesized using synthesis approaches described herein.

In some compositions of particular interest, the compositions can bedescribed by the formula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)M_(δ)O_(2−z)F_(z),where x ranges from about 0.05 to about 0.25, α ranges from about 0.1 toabout 0.4, β range from about 0.4 to about 0.65, γ ranges from about0.05 to about 0.3, δ ranges from about 0 to about 0.1 and z ranges fromabout 0 to about 0.1, and where M is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce,Y, Nb or combinations thereof. A person of ordinary skill in the artwill recognize that additional ranges of parameter values within theexplicit ranges above are contemplated and are within the presentdisclosure. The fluorine is a dopant that can contribute to cyclingstability as well as improved safety of the materials. In embodiments inwhich z=0, this formula reduces to Li_(1+x)Ni_(α)Mn_(β)Co_(γ)M_(δ)O₂. Ithas been found that suitable coatings provide desirable improvements incycling properties without the use of a fluorine dopant, although it maybe desirable to have a fluorine dopant in some embodiments. Furthermore,in some embodiments it is desirable to have δ=0 such that thecompositions are simpler while still providing improved performance. Forthese embodiments, if z=0 also, the formula simplifies toLi_(1+x)Ni_(α)Mn_(β)Co_(γ)O₂, with the parameters outlined above.

With respect to some embodiments of materials described herein, Thackeryand coworkers have proposed a composite crystal structure for somelithium rich metal oxide compositions in which a Li₂M′O₃ composition isstructurally integrated into a layered structure with a LiMO₂ component.The electrode materials can be represented in two component notation asa Li₂M′O₃ (1−a) LiMO₂, where M is one or more metal elements with anaverage valance of +3 and with at least one element being Mn or Ni andM′ is a metal element with an average valance of +4 and 0<a<l. Forexample, M can be a combination of Ni⁺², Co⁺³ and Mn⁺⁴. The overallformula for these compositions can be written asLi_(1+x)M′_(2x)M_(1−3x)O₂. Batteries formed from these materials havebeen observed to cycle at higher voltages and with higher capacitiesrelative to batteries formed with corresponding LiMO₂ compositions.These materials are described further in U.S. Pat. No. 6,680,143 toThackery et al., entitled Lithium Metal Oxide Electrodes for LithiumCells and Batteries,” and U.S. Pat. No. 6,677,082 to Thackery et al.,entitled “Lithium Metal Oxide Electrodes for Lithium Cells andBatteries,” both of which are incorporated herein by reference. Thackeryidentified Mn, Ti and Zr as being of particular interest as M′ and Mnand Ni for M.

The structure of some specific layered structures is described furtherin Thackery et al., “Comments on the structural complexity oflithium-rich Li_(1+x)M_(1−x)O₂ electrodes (M=Mn,Ni,Co) for lithiumbatteries,” Electrochemistry Communications 8 (2006), 1531-1538,incorporated herein by reference. The study reported in this articlereviewed compositions with the formulasLi_(1+x)[Mn_(0.5)Ni_(0.5)]_(1−x)O₂ andLi_(1+x)[Mn_(0.333)Ni_(0.333)Co_(0.333)]_(1−x)O₂. The article alsodescribes the structural complexity of the layered materials.

Recently, Kang and coworkers described a composition for use insecondary batteries with the formulaLi_(1+x)Ni_(α)Mn_(β)CO_(γ)M′_(δ)O_(2−z)F_(z), M=Mg, Zn, Al, Ga, B, Zr,Ti, x between about 0 and 0.3, α between about 0.2 and 0.6, β betweenabout 0.2 and 0.6, γ between about 0 and 0.3, δ between about 0 and 0.15and z between about 0 and 0.2. The metal ranges and fluorine wereproposed as improving battery capacity and stability of the resultinglayered structure during electrochemical cycling. See U.S. Pat. No.7,205,072, to Kang et al. (the '072 patent), entitled “Layered cathodematerials for lithium ion rechargeable batteries,” incorporated hereinby reference. This reference reported a cathode material with a capacitybelow 250 mAh/g (milli-ampere hours per gram) at room temperature after10 cycles, which is at an unspecified rate that can be assumed to be lowto increase the performance value. It is noted that if fluorine issubstituted for oxygen, the oxidation state of the multivalent metalsare lower relative to the oxidation state of the compositions withoutthe fluorine. Kang et al. examined various specific compositionsincluding Li_(1.2)Ni_(0.15)Mn_(0.55)Co_(0.1)O₂, which is similar to thecomposition examined in the examples below. The results obtained in the'072 patent involved a solid state synthesis of the materials that didnot achieve comparable cycling capacity of the batteries disclosed inthe examples below.

The performance of the positive electrode active materials is influenceby many factors. The mean particle size and the particle sizedistribution are two of the basic properties characterizing the positiveelectrode active materials, and these properties influence the ratecapabilities and tap densities of the materials. Because batteries havefixed volumes, it is therefore desirable that the material used in thepositive electrode of these batteries has a high tap density if thespecific capacity of the material can be maintained at a desirably highvalue. Then, the total capacity of the battery can be higher due to thepresence of more chargeable material in the positive electrode.

Synthesis Methods

Synthesis approaches described herein can be used to form layeredlithium rich cathode active materials with improved specific capacityupon cycling and a high tap density. The synthesis methods have beenadapted for the synthesis of compositions with the formulaLi_(1+x)Ni_(α)Mn_(β)Co_(γ)M_(δ)O_(2−z)F_(z), ranges from about 0.05 toabout 0.25, α ranges from about 0.1 to about 0.4, β ranges from about0.4 to about 0.65, γ ranges from about 0.05 to about 0.3, δ ranges fromabout 0 to about 0.1 and z ranges from about 0 to about 0.1, and where Mis Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb or combinations thereof. Thesynthesis approaches are also suitable for commercial scale up.Specifically, co-precipitation process can be used to synthesize thedesired lithium rich positive electrode materials with desirableresults. A lithium fluoride reactant can be added to the reactants,generally along with an appropriate amount of lithium hydroxide, tointroduce a fluorine dopant. Alternatively or additionally, a solutionassisted precipitation method discussed in detail below can be used tocoat the material with metal fluoride.

In the co-precipitation process, metal salts are dissolved into anaqueous solvent, such as purified water, with a desired molar ratio.Suitable metal salts include, for example, metal acetates, metalsulfates, metal nitrates, and combination thereof. The concentration ofthe solution is generally selected between 1M and 3M. The relative molarquantities of metal salts can be selected based on the desired formulafor the product materials. The pH of the solution can then be adjusted,such as with the addition of Na₂CO₃ and/or ammonium hydroxide, toprecipitate a metal carbonate with the desired amounts of metalelements. Generally, the pH can be adjusted to a value between about 6.0to about 9.0. The solution can be heated and stirred to facilitate theprecipitation of the carbonate. The precipitated metal carbonate canthen be separated from the solution, washed and dried to form a powderprior to further processing. For example, drying can be performed in anoven at about 110° C. for about 4 to about 12 hours. A person ofordinary skill in the art will recognize that additional ranges ofprocess parameters within the explicit ranges above are contemplated andare within the present disclosure.

The collected metal carbonate powder can then be subjected to a heattreatment to convert the carbonate composition to the correspondingoxide composition with the elimination of carbon dioxide. Generally, theheat treatment can be performed in an oven, furnace or the like. Theheat treatment can be performed in an inert atmosphere or an atmospherewith oxygen present. In some embodiments, the material can be heated toa temperature of at least about 350 ° C. and in some embodiments fromabout 400 ° C. to about 800 ° C. to convert the carbonate to an oxide.The heat treatment generally can be performed for at least about 15minutes, in further embodiments from about 30 minutes to 24 hours orlonger, and in additional embodiments from about 45 minutes to about 15hours. A further heat treatment can be performed to improve thecrystallinity of the product material. This calcination step for formingthe crystalline product generally is performed at temperatures of atleast about 650 ° C., and in some embodiments from about 700° C. toabout 1200° C., and in further embodiments from about 700 ° C. to about1100° C. The calcination step to improve the structural properties ofthe powder generally can be performed for at least about 15 minutes, infurther embodiments from about 20 minutes to about 30 hours or longer,and in other embodiments from about 1 hour to about 36 hours. Theheating steps can be combined, if desired, with appropriate ramping ofthe temperature to yield desired materials. A person of ordinary skillin the art will recognize that additional ranges of temperatures andtimes within the explicit ranges above are contemplated and are withinthe present disclosure.

The lithium element can be incorporated into the material at one or moreselected steps in the process. For example, a lithium salt can beincorporated into the solution prior to or upon performing theprecipitation step through the addition of a hydrated lithium salt. Inthis approach, the lithium species is incorporated into the carbonatematerial in the same way as the other metals. Also, due to theproperties of lithium, the lithium element can be incorporated into thematerial in a solid state reaction without adversely affecting theresulting properties of the product composition. Thus, for example, anappropriate amount of lithium source generally as a powder, such asLiOH.H₂O, LiOH, Li₂CO₃, or a combination thereof, can be mixed with theprecipitated metal carbonate. The powder mixture is then advancedthrough the heating step(s) to form the oxide and then the crystallinefinal product material.

Coatings and Methods for Forming the Coatings

Metal fluoride coatings have been found to significantly improve theperformance of the lithium rich layered positive electrode activematerials described herein. In particular, the cycling properties of thebatteries formed from the metal fluoride coated lithium metal oxide havebeen found to significantly improve from the uncoated material.Additionally, the overall capacity of the batteries also shows desirableproperties with the fluoride coating, and the irreversible capacity lossof the first cycle of the battery is reduced. As discussed earlier,first cycle irreversible capacity loss of a battery is the differencebetween the charge capacity of the new battery and its first dischargecapacity. The bulk of the first cycle irreversible capacity loss isgenerally attributed to the positive electrode material.

The coating provides an unexpected improvement in the performance of thehigh capacity lithium rich compositions described herein. In general, aselected metal fluoride or metalloid fluoride can be used for thecoating. Similarly, a coating with a combination of metal and/ormetalloid elements can be used. Metal/metalloid fluoride coatings havebeen proposed to stabilize the performance of positive electrode activematerials for lithium secondary batteries. Suitable metals and metalloidelements for the fluoride coatings include, for example, Al, Bi, Ga, Ge,In, Mg, Pb, Si, Sn, Ti, Tl, Zn, Zr and combinations thereof. Aluminumfluoride can be a desirable coating material since it has a reasonablecost and is considered environmentally benign. The metal fluoridecoating are described generally in published PCT application WO2006/109930A to Sun et al., entitled “Cathode Active Materials Coatedwith Fluorine Compound for Lithium Secondary Batteries and Method forPreparing the Same,” incorporated herein by reference. This patentapplication provides results for LiCoO₂ coated with LiF, ZnF₂ or AlF₃.The Sun PCT application referenced above specifically refers to thefollowing fluoride compositions, CsF, KF, LiF, NaF, RbF, TiF, AgF, AgF₂,BaF₂, CaF₂, CuF₂, CdF₂, FeF₂, HgF₂, Hg₂F₂, MnF₂, MgF₂, NiF₂, PbF₂, SnF₂,SrF₂, XeF₂, ZnF₂, AlF₃, BF₃, BiF₃, CeF₃, CrF₃, DyF₃, EuF₃, GaF₃, GdF₃,FeF₃, HoF₃, InF₃, LaF₃, LuF₃, MnF₃, NdF₃, VOF₃, PrF₃, SbF₃, ScF₃, SmF₃,TbF₃, TiF₃, TmF₃, YF₃, YbF₃, TlF₃, CeF₄, HfF₄, SiF₄, SnF₄, TiF₄, VF₄,ZrF₄, NbF₅, SbF₅, TaF₅, BiF₅, MoF₆, ReF₆, SF₆, and WF₆.

The effect of an AlF₃ coating on the cycling performance ofLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ is described further in an article to Sunet al., “AlF₃-Coating to Improve High Voltage Cycling Performance ofLi[Ni_(1/3)Co_(1/3)Mn_(1/3)]O₂ Cathode Materials for Lithium SecondaryBatteries,” J. of the Electrochemical Society, 154 (3), A168-A172(2007). Also, the effect of an AlF₃ coating on the cycling performanceof LiNi_(0.8)Co_(0.1)Mn_(0.1)O₂ is described further in an article toWoo et al., “Significant Improvement of Electrochemical Performance ofAlF₃-Coated Li[Ni_(0.8)Co_(0.1)Mn_(0.1)]O₂ Cathode Materials,” J. of theElectrochemical Society, 154 (11) A1005-A1009 (2007), incorporatedherein by reference. A reduction in irreversible capacity loss was notedwith Al₂O₃ coatings by Wu et al., “High Capacity, Surface-ModifiedLayered Li[Li_((1−x)/3)Mn_((2−x)/3)Ni_(x/3)Co_(x/3)]O₂ Cathodes with LowIrreversible Capacity Loss,” Electrochemical and Solid State Letters, 9(5) A221-A224 (2006), incorporated herein by reference.

It has been found that metal/metalloid fluoride coatings cansignificantly improve the performance of lithium rich layeredcompositions for lithium ion secondary batteries as demonstrated in theexamples below. The coating improves the capacity of the batteries.However, the coating itself is not electrochemically active. When theloss of specific capacity due to the amount of coating added to a sampleexceeds where the benefit of adding coating is offset by itselectrochemical inactivity, reduction in battery capacity can beexpected. In general, the amount of coating can be selected to balancethe beneficial stabilization resulting from the coating with the loss ofspecific capacity due to the weight of the coating material thatgenerally does not contribute directly to a high specific capacity ofthe material. In general, the amount of coating material ranges fromabout 0.01 mole percent to about 10 mole percent, in further embodimentsfrom about 0.1 mole percent to about 7 mole percent, in additionalembodiments from about 0.2 mole percent to about 5 mole percent, and inother embodiments from about 0.5 mole percent to about 4 mole percent. Aperson of ordinary skill in the art will recognize that additionalranges of coating material within the explicit ranges above arecontemplated and are within the present disclosure. The amount of AlF₃effective in AlF₃ coated metal oxide materials to improve the capacityof the uncoated material is related to the particle size and surfacearea of the uncoated material. In particular, a higher mole percentageof metal fluoride coating generally can be used for a higher surfacearea powder to achieve an equivalent effect relative to a coating on alower surface area powder.

The fluoride coating can be deposited using a solution basedprecipitation approach. A powder of the positive electrode material canbe mixed in a suitable solvent, such as an aqueous solvent. A solublecomposition of the desired metal/metalloid can be dissolved in thesolvent. Then, NH₄F can be gradually added to the dispersion/solution toprecipitate the metal fluoride. The total amount of coating reactantscan be selected to form the desired amount of coating, and the ratio ofcoating reactants can be based on the stoichiometry of the coatingmaterial. The coating mixture can be heated during the coating processto reasonable temperatures, such as in the range from about 60° C. toabout 100° C. for aqueous solutions for from about 20 minutes to about48 hours, to facilitate the coating process. After removing the coatedelectroactive material from the solution, the material can be dried andheated to temperatures generally from about 250° C. to about 600° C. forabout 20 minutes to about 48 hours to complete the formation of thecoated material. The heating can be performed under a nitrogenatmosphere or other substantially oxygen free atmosphere.

Battery Performance

Batteries formed from the improved positive electrode active materialsdescribed herein have demonstrated superior performance under realisticdischarge conditions for moderate current applications. Specifically,the active materials have exhibited high tap density and demonstrated animproved specific capacity upon cycling of the batteries at moderatedischarge rates. Furthermore, the coated materials have demonstratedimproved cycling out to a large number of cycles. In some embodiments,coated electroactive materials demonstrate a significant reduction inthe first cycle irreversible capacity loss relative to the uncoatedmaterials.

In general, various similar testing procedures can be used to evaluatethe battery performance. A specific testing procedure is described forthe evaluation of the performance values described herein. The testingprocedure is described in more detail in the examples below.Specifically, the battery can be cycled between 4.6 volts and 2.0 voltsat room temperature, although other ranges can be used withcorrespondingly different results. The evaluation over the range from4.6 volts to 2.0 volts is desirable for commercial use since thebatteries generally have stable cycling over this voltage range. For thefirst three cycles, a battery is discharged at a rate of C/10 toestablish irreversible capacity loss. The battery is then cycled forthree cycles at C/5. For cycle 7 and beyond, the battery is cycled at arate of C/3, which is a reasonable testing rate for medium currentapplications. Again, the notation C/x implies that the battery isdischarged at a rate to fully discharge the battery to the selectedvoltage minimum in x hours. The battery capacity depends significantlyon the discharge rate, with lose of capacity as the discharge rateincreases.

In some embodiments, the positive electrode active material has aspecific capacity during the tenth cycle at a discharge rate of C/3 ofat least about 235 milliamp hours per gram (mAh/g), in additionalembodiments from about 240 mAh/g to about 310 mAh/g, in furtherembodiments from about 245 mAh/g to about 300 mAh/g and in otherembodiment from about 250 mAh/g to about 290 mAh/g. Additionally, the20^(th) cycle discharge capacity of the material is at least about 98%,and in further embodiments 98.5% of the 5^(th) cycle discharge capacity,cycled at a discharge rate of C/3. The first cycle irreversible capacityloss for the coated electroactive materials can be decreased at leastabout 25%, and in further embodiments from about 30% to about 60%relative to the equivalent performance of the uncoated materials. Thetap density of the material, which is measured as described below, canbe at least about 1.8 g/mL, in further embodiments from about 2 to about3.5 g/mL and in additional embodiments from about 2.05 to about 2.75g/mL. High tap density translates into high overall capacity of abattery given a fixed volume. A person of ordinary skill in the art willrecognize that additional ranges of specific capacity and tap densityand of decreases in irreversible capacity loss are contemplated and arewithin the present disclosure. For fixed volume applications such asbatteries for electronic devices, high tap density therefore highoverall capacity of the battery is of particular significance.

Generally, tap density is the apparent powder density obtained understated conditions of tapping. The apparent density of a powder dependson how closely individual particles of the powder are pack together. Theapparent density is affected not only by the true density of the solids,but by the particle size distribution, particle shape and cohesiveness.Handling or vibration of powdered material can overcome some of thecohesive forces and allow particles to move relative to one another sosmaller particles can work their way into the spaces between the largerparticles. Consequently, the total volume occupied by the powderdecreases and its density increases. Ultimately no further naturalparticle packing can be measured without the addition of pressure andmaximum particle packing has been achieved. While electrodes are formedwith the addition of pressure, a reasonably amount of pressure is onlyeffective to form a certain packing density of the electroactivematerials in the battery electrode. The actual density in the electrodegenerally relates to the tap density measured for a powder so that thetap density measurements are predictive of the packing density in abattery electrode with a higher tap density corresponding to a higherpacking density in the battery electrode.

Under controlled conditions of tap rate, drop height and container size,the tap density obtained can be highly reproducible. The tap density ofa positive electrode active material described herein can be measured byusing graduated measuring cylinders on a commercially available tapmachine with pre-determined tapping parameters. The specific method formeasurement of the tap density for the measurements described herein isprovided explicitly in Example 3.

EXAMPLES

The coin cell batteries tested in Examples 1-3 were all performed usingcoin cell batteries produced following a procedure outlined here. Thelithium metal oxide (LMO) powders were mixed thoroughly with acetyleneblack (Super P™ from Timcal, Ltd, Switzerland) and graphite (KS 6™ fromTimcal, Ltd) to form a homogeneous powder mixture. Separately,Polyvinylidene fluoride PVDF (KF1300™ from Kureha Corp., Japan) wasmixed with N-methyl-pyrrolidone (Honeywell-Riedel-de-Haen) and stirredovernight to form a PVDF-NMP solution. The homogeneous powder mixturewas then added to the PVDF-NMP solution and mixed for about 2 hours toform homogeneous slurry. The slurry was applied onto an aluminum foilcurrent collector to form a thin wet film using a doctor's blade coatingprocess.

A positive electrode material was formed by drying the aluminum foilcurrent collector with the thin wet film in vacuum oven at 110° C. forabout two hours to remove NMP. The positive electrode material waspressed between rollers of a sheet mill to obtain a positive electrodewith desired thickness. An example of a positive electrode compositiondeveloped using above process having a LMO:acetylene black:graphite:PVDFratio of 80:5:5:10 is presented below.

The positive electrode was placed inside an argon filled glove box forthe fabrication of the coin cell batteries. Lithium foil (FMC Lithium)having thickness of 125 micron was used as a negative electrode. Theelectrolyte was a 1 M solution of LiPF₆ form by dissolving LiPF₆ salt ina mixture of ethylene carbonate, diethyl carbonate and dimethylcarbonate (from Ferro Corp., Ohio USA) at a 1:1:1 volumetric ratio. Atrilayer (polypropylene/polyethylene/polypropylene) micro-porousseparator (2320 from Celgard, LLC, NC, USA) soaked with electrolyte wasplaced between the positive electrode and the negative electrode. A fewadditional drops of electrolyte were added between the electrodes. Theelectrodes were then sealed inside a 2032 coin cell hardware (HohsenCorp., Japan) using a crimping process to form a coin cell battery. Theresulting coin cell batteries were tested with a Maccor cycle tester toobtain charge-discharge curve and cycling stability over a number ofcycles. All the electrochemical data contained herein have been cyclingat three rates, 0.1 C (C/10), 0.2 C (C/5) or 0.33 C (C/3).

Example 1 Reaction of Metal Sulfate with Na₂CO₃/NH₄OH for CarbonateCo-precipitation

This example demonstrates the formation of a desired cathode activematerial using a carbonate co-precipitation process. Stoichiometricamounts of metal sulfates (NiSO₄.xH₂O, CoSO₄.xH₂O, & MnSO₄.xH₂O) weredissolved in distilled water to form a metal sulfate aqueous solution.Separately, an aqueous solution containing Na₂CO₃ and NH₄OH wasprepared. For the formation of the samples, the two solutions weregradually added to a reaction vessel to form metal carbonateprecipitates. The reaction mixture was stirred, and the temperature ofthe reaction mixture was kept at a temperature between room temperatureand 80° C. The pH of the reaction mixture was in the range from 6-9. Ingeneral, the aqueous metal sulfate solution had a concentration from 1Mto 3M, and the aqueous Na₂CO₃/NH₄OH solution had a Na₂CO₃ concentrationof 1M to 4M and a NH₄0H concentration of 0.2-2M. The metal carbonateprecipitate was filtered, washed multiple times with distilled water,and dried at 110° C. for about 16 hrs to form a metal carbonate powder.Optical microscope images of a representative metal carbonate powder isshown in FIG. 2, indicating the precursor particles formed have asubstantially spherical shape and are relatively homogenous with respectto size distribution. Specific ranges of reaction conditions for thepreparation of the samples are further outlined in Table 1.

TABLE 1 Reaction Process Condition Values Reaction pH 6.0-9.0 Reactiontime 0.1-24 hr Reactor type Batch Reactor agitation speed 200-1400 rpmReaction temperature RT - 80° C. Concentration of the metal salts 1-3MConcentration of Na₂CO₃ (precipitating agent) 1-4M Concentration ofNH₄OH (chelating agent) 0.2-2M Flow rate of the metal salts 1-100 mL/minFlow rate of Na₂CO₃ & NH₄OH 1-100 mL/min

An appropriate amount of Li₂CO₃ powder was combined with the dried metalcarbonate powder and thoroughly mixed by a Jar Mill, double planetarymixer, or dry powder rotary mixer to form a homogenous powder mixture. Aportion, e.g. 5 grams, of the homogenized powders is calcined followedby an additional mixing step to further homogenize the powder formed.The further homogenized powder was again calcined to form the lithiumcomposite oxide. The product composition was determined to beLi_(1.2)Ni_(0.175)Co_(0.10)Mn_(0.525)O₂. Specific ranges of calcinationconditions are further outlined in Table 2.

TABLE 2 Calcination Process Condition Values 1^(st) Step temperature400-800° C. time 1-24 hr protective gas Nitrogen or Air Flow rate ofprotective gas 0-50 scfh 2^(nd) Step temperature 700-1100° C. time 1-36hr protective gas Nitrogen or Air Flow rate of protective gas 0-50 scfh

SEM micrograms at different magnifications of the lithium compositeoxide are shown in FIG. 3, indicating the particles formed have asubstantially spherical shape and are relatively homogenous in size. Thex-ray diffraction pattern of the composite powder is shown in FIG. 4,showing characteristics of a rock-salt type structure. The composite wasused to form a coin cell battery following the procedure outlined above.The coin cell battery was tested and the plot of voltage versus specificcapacity at discharge rate of 0.1 C and 0.33 C of the first cycle areshown in FIG. 5(a) & (b), respectively. The first cycle specificcapacity of the battery at 0.1 C discharge rate is around 255 mAh/g. Thefirst cycle specific capacity of the battery at 0.33 C discharge rate isaround 240 mAh/g. Specific capacity versus cycle life of the coin cellbattery is also tested and the results are shown in FIG. 6. The firstthree cycles were measured at a discharge rate of 0.1 C. The next threecycles were measured at a rate of 0.2 C. The subsequent cycles weremeasured at a rate of 0.33 C.

Example 2 Formation of AlF₃ Coated Metal Oxide Materials

The metal oxide particles prepared in the above example can be coatedwith a thin layer of aluminum fluoride (AlF₃) using a solution-basedmethod. For a selected amount of aluminum fluoride coating, appropriateamount of saturated solution of aluminum nitrate was prepared in anaqueous solvent. The metal oxide particles were then added into thealuminum nitrate solution to form a mixture. The mixture was mixedvigorously for a period of time to homogenize. The length of mixingdepends on the volume of the mixture. After homogenization, astoichiometric amount of ammonium fluoride was added to the homogenizedmixture to form aluminum fluoride precipitate while retaining the sourceof fluorine. Upon the completion of the precipitation, the mixture wasstirred at 80° C. for 5 h. The mixture was then filtered and the solidobtained was washed repeatedly to remove any un-reacted materials. Thesolid was calcined in nitrogen atmosphere at 400° C. for 5 h to form theAlF₃ coated metal oxide material.

Specifically, samples of lithium metal oxide (LMO) particles synthesizedas described in example 1 were coated with 1.0 mole % aluminum fluorideusing the process described in this example. The x-ray diffractionpattern of the 1.0 mole % aluminum fluoride coated LMO sample is shownin FIG. 7. The aluminum fluoride coated LMOs were then used to form coincell batteries following the procedure outlined above. The coin cellbatteries were tested, and the plots of voltage versus specific capacityof the coin cell batteries at discharge rate of 0.1 C and 0.33 are shownin FIG. 8(a) and FIG. 8(b), respectively. The first cycle specificcapacity of the battery at 0.1 C discharge rate is around 285 mAh/g. Thefirst cycle specific capacity of the battery at 0.33 C discharge rate isaround 265 mAh/g. Specific capacity versus cycle life of the coin cellbatteries also tested and the results are shown in FIG. 9. The resultsare compared to the results of a corresponding uncoated sample and shownin FIG. 10. As shown in FIG. 10, coin cell battery made from sample with1.0 mole % aluminum fluoride coating has higher capacity than coin cellbattery made from uncoated sample. Generally, for testing the coin cellbatteries, the first three cycles were measured at a discharge rate of0.1 C. The next three cycles were measured at a rate of 0.2 C. Thesubsequent cycles were measured at a rate of 0.33 C.

Irreversible capacity loss (IRCL) of the uncoated and AlF₃ coatedsamples are also compared. As shown in Table 3, uncoated sample has IRCLof 64.26 mAh/g, which is significantly higher than the IRCL of 31.7mAh/g of 1.0 mole % AlF₃ coated sample.

TABLE 3 1st C/10 Charge 1st C/10 Discharge IRCL (mAh/g) (mAh/g) (mAh/g)Uncoated 321.92 257.66 64.26 1% AlF3 coated 317.49 285.78 31.71

Example 3 Tap Density Results of Different Metal Oxide Materials

An AUTOTAP™ machine from Quantachrome Instruments was used to measuretap density of the samples synthesized in examples 1 and 2. In a typicalmeasurement process, a 4 gram quantity of sample powder was weighed outand placed in a graduated cylinder (10 mL). The cylinder was thenmounted on a wheel of the AUTOTAP™ that taps at a tap rate of 260 min⁻¹with a drop height of 3 mm. After 2000 taps the volume of the powder wasdetermined by using the measurement markings on the graduated cylinder.The initial weight of the sample divided by the measured volume aftertapping gives the tap density in g/mL unit of the sample. The tapdensities of samples prepared as described in Example 1 were measuredand the tap densities of 2.0, 2.1 and 2.2 have been obtained. Ingeneral, samples with tap density around and above 1.8 g/mL can alsohave 10^(th) cycle specific capacity around and above 235 mAh/g at 0.33C. In some embodiments, samples with tap density around and above 2.0g/mL have 10^(th) cycle specific capacity around and above 240 mAh/g at0.33 C.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, although thepresent invention has been described with reference to particularembodiments, those skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and scope ofthe invention. Any incorporation by reference of documents above islimited such that no subject matter is incorporated that is contrary tothe explicit disclosure herein.

1. A positive electrode active material for a lithium ion battery havinga 10^(th) cycle specific discharge capacity of at least 235 mAh/g atroom temperature and a tap density of at least 1.8 g/mL, wherein thespecific discharge capacity is determined at a discharge rate of C/3when discharged from 4.6 volts to 2.0 volts.
 2. The positive electrodeactive material of claim 1 comprising a composition having a formula ofxLiMO₂·(1−x) Li₂M′O₃, where M represents one or more metal ions havingan average valance of +3 and M′ represents one or more metal ions havingan average valance of +4 and 0<x<1.
 3. The positive electrode materialof claim 2 wherein M′ comprises Mn and M comprises Mn, Co and Ni.
 4. Thepositive electrode material of claim 1 comprising a composition with aformula Li_(1+x)Ni_(α)Mn_(β)Co_(γ)O₂, where x ranges from about 0.05 toabout 0.25, α ranges from about 0.1 to about 0.4, β ranges from about0.4 to about 0.65, and γ ranges from about 0.05 to about 0.3.
 5. Thepositive electrode material of claim 1 comprising a composition with aformula Li_(1.2)Ni_(0.175)Co_(0.10)Mn_(0.525)O₂.
 6. The positiveelectrode active material of claim 1 comprising a first material havinga formula of xLiMO₂ (1−x) Li₂M═O₃, where M represents one or more metalions having an average valance of +3 and M′ represents one or more metalions having an average valance of +4 and 0<x<1 and a metal fluoridecoating on the first material.
 7. The positive electrode material ofclaim 1 having a formula Li_(1+x)Ni_(α)Mn_(β)CO_(γ)M″_(δ)O_(2−z)F_(z),where x ranges from about 0.05 to about 0.25, α ranges from about 0.1 toabout 0.4, β ranges from about 0.4 to about 0.65, γ ranges from about0.05 to about 0.3, δ ranges from about 0 to about 0.1 and z ranges fromabout 0 to about 0.1, and where M″ is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce,Y, Nb or combinations thereof.
 8. The positive electrode active materialof claim 1 wherein the material comprises from about 0.1 mole percent toabout 4 mole percent metal fluoride.
 9. The positive electrode activematerial of claim 8 wherein the metal fluoride comprises AlF₃.
 10. Thepositive electrode active material of claim 1 wherein the material has a10th cycle discharge capacity from about 240 mAh/g to about 310 mAh/g atroom temperature at a discharge rate of C/3 when discharged from 4.6volts to 2.0 volts.
 11. The positive electrode active material of claim1 wherein the material has a 10th cycle discharge capacity from about250 mAh/g to about 290 mAh/g at room temperature at a discharge rate ofC/3 when discharged from 4.6 volts to 2.0 volts.
 12. The positiveelectrode active material of claim 1 having a tap density of at least2.0 g/mL.
 13. A secondary lithium ion battery comprising a positiveelectrode comprising the positive electrode active material of claim 1,a negative electrode comprising a lithium intercalation composition anda separator between the positive electrode and the negative electrode.14. A positive electrode active material for a lithium ion batterycomprising, a layered lithium metal oxide composite comprising +4 metalcations, +3 metal cations and +2 metal cations within a crystallinelattice, and a metal/metalloid fluoride coating on the lithium metaloxide composite, wherein the first cycle irreversible capacity loss ofthe electrode material is no more than about 2/3 of the first cycleirreversible capacity loss of the uncoated lithium metal oxidecomposite, both cycled at discharge rate of C/10, wherein the 20^(th)cycle discharge capacity of the electrode material is at least about 98%of the 5th cycle discharge capacity when discharged at room temperatureat a discharge rate of C/3, and wherein the electrode material has a tapdensity of at least 1.8 g/mL.
 15. The positive electrode active materialof claim 14 wherein the uncoated lithium metal oxide composite has aformula of xLiMO₂ (1−x) Li₂M′O₃, where M represents one or more metalions having an average valance of +3 and M′ represents one or more metalions having an average valance of +4, 0<x<1.
 16. The positive electrodematerial of claim 15 wherein M′ comprises Mn and M comprises Mn, Co andNi.
 17. The positive electrode material of claim 14 having a formulaLi_(1+x)Ni_(α)Mn_(β)CO_(γ)M_(δ)O_(2−z)F_(z), where x ranges from about0.05 to about 0.25, α ranges from about 0.1 to about 0.4, β ranges fromabout 0.4 to about 0.65, γ ranges from about 0.05 to about 0.3, δ rangesfrom about 0 to about 0.1 and z ranges from about 0 to about 0.1, andwhere M is Mg, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb or combinationsthereof.
 18. The positive electrode active material of claim 14 whereinthe material comprises from about 0.1 mole percent to about 4 molepercent metal fluoride.
 19. The positive electrode active material ofclaim 14 wherein the metal fluoride comprises AlF₃.
 21. The positiveelectrode active material of claim 14 wherein the material has a 20thcycle discharge capacity that is at least about 98.5% of the 5th cycledischarge capacity when discharged at room temperature at a dischargerate of C/3.
 22. The positive electrode active material of claim 14wherein the material has a 10th cycle discharge capacity from about 250mAh/g to about 310 mAh/g at room temperature at a discharge rate of C/3when discharged from 4.6 volts to 2.0 volts.
 23. The positive electrodeactive material of claim 14 having a 10^(th) cycle specific dischargecapacity of at least 260 mAh/g at room temperature, wherein the specificdischarge capacity is determined at a discharge rate of C/3 whendischarged from 4.6 volts to 2.0 volts.
 24. The positive electrodeactive material of claim 14 having a tap density of at least 2.0 g/mL.25. A secondary lithium ion battery comprising a positive electrodecomprising the positive electrode active material of claim 14, anegative electrode comprising a lithium intercalation composition and aseparator between the positive electrode and the negative electrode.